Personal care compositions which can suspend beads and/or other particles are very desirable. The suspended materials can add a number of beneficial uses which include, but are certainly not limited to: abrasion, visual impact (e.g., optical particles), encapsulates.
Typically, particles are suspended in personal care compositions using structuring systems such as acrylate polymers, structuring gums (e.g., xanthan gum), starch, agar, hydroxyl alkyl cellulose, etc. When large particles are suspended (e.g., polyethylene particles, guar beads etc.), the level of polymer used is typically 1% or more. These high polymer levels increase the cost of the formulation, and it would be desirable to find suspending polymers which suspend, even when used in smaller amounts.
Applicants have now found suspending polymers which, when used in the personal care liquid compositions of the invention, quite unpredictably provide tremendous structuring efficiency (e.g., suspend high amount of beads, particles, etc., even relatively large size particles, at low levels of polymer); provide excellent rheological properties (e.g., high zero or low shear viscosity and low high shear viscosity); and are salt tolerant, if salt is used in the formulation.
More specifically, the microfibrous cellulose of the invention provides excellent suspending properties when used at low levels (0.01-1%, preferably 0.02-0.5% by wt.) for suspending particles as large as 3000 microns; of course it can be used at even lower levels to suspend smaller particles (1-1000, preferably 1-800 microns).
In particular, the microfibrous cellulose can be used in compositions with 0.5-40% surfactant where, whether low or high amounts of surfactant are used to provide structuring/suspension ability, small amounts of suspending polymer of the invention can be used. A further benefit is that, in the presence of salt (added to help the surfactant structure, for example, to form rod-like to worm-like micelles and therefore enhance structure/suspension even further), the suspending polymer does not lose its suspending effect. This contrasts with many other suspending polymers which tend to be salt intolerant and lose suspending powers. In addition the polymer can be used to form transparent liquid compositions.
In general, cellulose is an organic compound with formula (C6H10O5)n. It is a structural polysaccharide derived from beta glucose and is the primary structural component of green plants.
Traditionally, cellulose is harvested from plant resources (e.g., cotton, wood). The cellulose is assembled from glucose, which glucose is produced in the living plant cell from photosynthesis. Cellulose may also be made by photosynthetic plant microbes, such as unicellular plankton or algae found in the ocean.
Cellulose can also be assembled by bacteria. However, the bacteria is typically devoid of photosynthetic capacity and usually requires glucose or organic substrate synthesized by a photosynthetic organism to assemble cellulose. Some bacteria can use methane or sulfur substrates to produce glucose and other organic substrates for cellulose (see “Microbial Cellulose: A New resource for Wood, Paper, Textile, Food and Specialty Products”, by R. M. Brown Jr., (http://www.botany.utexas.edu/facstaff/facpages/mbrown/position1.htm)
One bacteria for example, Acetobacter xylinum, is a non-photosynthetic organism which can procure glucose sugar etc. and convert into cellulose. As noted in the reference cited, a cell of acetobacter has a linear row of pores from which glucan chain polymer aggregates are spun. The pores can produce a cable of polymers resulting in cellulose “ribbons” and these are spun into fibrils.
These type of bacterially produced microfibrous cellulose polymers, as noted in the reference to Brown, Jr., have been contemplated for use in industries including the food industry and healthcare. It is also noted from the reference that the polymers could be used for skin creams.
Nowhere that applicants are aware, however, have these type of polymers been contemplated for use in personal wash liquid cleanser compositions. Nor would it be predictable that these polymers would have such tremendous suspension ability when used in personal wash liquid cleanser.
Unexpectedly and quite unpredictably, however, applicants have now found that microfibrous cellulose can be used in small amount (e.g., 0.01 to 1.0%, preferably 0.1-0.5% by wt.) to suspend, for example, capsules, particles, air bubbles, from 1-3000μ in size, while maintaining desired rheological properties (i.e., high zero shear viscosity, as required for suspending and low high shear viscosity as required for ready pourability). Further these unbelievably efficient polymers are salt tolerant (while not wishing to be bound by theory, this is believed to be true because the polymers are nonionic), and can be used for preparing transparent compositions.